Research and development aimed at increase in efficiency and output of semiconductor light-emitting elements including a LED chip in which a light-emitting layer is formed from a nitride semiconductor material (GaN, InGaN, AlGaInN, etc.) have been heretofore widely conducted. Research and development of light-emitting devices emitting mixed color light with a different color from that of an emission color of semiconductor light-emitting elements have also been widely conducted by combining the semiconductor light-emitting elements of this type with fluorescent materials, and abundant research and development have been performed to expand the application of such light-emitting devices to a general illumination field. Such light-emitting devices use the fluorescent material as a wavelength conversion material that is excited by light emitted from the semiconductor light-emitting element and emits light with a wavelength longer than that of the semiconductor light-emitting element. Commercially, for example, such light-emitting devices have been produced as white light-emitting devices (typically referred to as white LED) for obtaining white color light (emission spectrum of white light) by combining a semiconductor light-emitting element emitting blue light or violet light and a fluorescent material.
A configuration in which a fine peak-valley structure is formed by providing pyramidal protrusions of a several micron size on the surface side of an n-type GaN film 22′ of a semiconductor light-emitting element, for example, as shown in FIG. 8, has been suggested for efficiently taking out (extracting) the light emitted from the light-emitting layer to the outside with the object of increasing the light output of the above-described semiconductor light-emitting element. In the semiconductor light-emitting element shown in FIG. 8, a light-emitting layer 2′ has a laminated structure of a p-type GaN film 24′, a light-emitting film 23′ and the n-type GaN film 22′, and yet the p-type GaN film 24′ is bonded to the top surface of a Si substrate 6′, with a metal film 7′ being interposed therebetween, and an anode 5′ is formed on the lower surface of the Si substrate 6′. In this configuration, the metal film 7′ plays a role of ensuring ohmic electric conductivity between the p-type GaN film 24′ and the Si substrate 6′, a role of reflecting the light that has passed through the p-type GaN film 24′ towards the light-emitting film 23′ side, and a role of joining the p-type GaN film 24′ and the Si substrate 6′.
However, in the case that the fine peak-valley structure is formed over the entire upper surface of the n-type GaN film 22′ as well as an island-like cathode 4′ composed of a laminated film including, for example, a Ti film, an Al film and a Au film, is formed on the top surface of the n-type GaN film 22′, as in the semiconductor light-emitting element of the configuration shown in FIG. 8, the light incoming from the n-type GaN film 22′ side is easily absorbed and light emission efficiency is decreased. Further, in the semiconductor light-emitting element shown in FIG. 8, a reflectance of the metal film 7′ can be increased to increase the light extraction efficiency. However in this case, it is necessary to maintain the electric conductivity and bonding strength, therefore, the yield drops and the productivity decreases.
Further, in the semiconductor light-emitting element shown in FIG. 8, the pyramidal protrusions are formed by performing crystal anisotropic etching of the n-type GaN film 22′ by using a KOH solution. Therefore, the size and density of pyramidal protrusions strongly depend on such as crystallinity of the n-type GaN film 22′, reproducibility of size and density of the pyramidal protrusions is low, and the light extraction efficiency causes a variation, therefore the light-emission efficiency causes a variation, and cost is increased due to drop of the yield.
Further, a semiconductor light-emitting element as shown in FIG. 9 has also been suggested, in which a fine peak-valley structure 8a′ is formed on the upper surface of a sapphire substrate 8′ as well as a light-emitting layer 2′ having a laminated structure including an n-type GaN film 22′, a light-emitting film 23′ and a p-type GaN film 24′ is formed on the upper surface of the sapphire substrate 8′. In the semiconductor light-emitting element shown in FIG. 9, a transparent conductive film 25′ composed of an ITO film is formed over the entire upper surface of the p-type GaN film 24′, an island-like anode 5′ is formed on the transparent conductive film 25′, and an island-like cathode 4′ is formed on upper surface of the n-type GaN film 22′. In the semiconductor light-emitting element shown in FIG. 9, the island-like cathode 4′ is formed on the surface of the n-type GaN film 22′ after being exposed by etching a predetermined region of the laminated film including the n-type GaN film 22′, the light-emitting film 23′ and the p-type GaN film 24′ formed on the upper surface of the sapphire substrate 8′.
In the semiconductor light-emitting device shown in FIG. 9, the fine peak-valley structure 8a′ is formed on the interface between the sapphire substrate 8′ and the n-type GaN film 22′, and the light extraction efficiency is raised and light emission efficiency is increased by changing the propagation direction of light inside the semiconductor light-emitting element by the fine peak-valley structure 8a′. 
However, in the semiconductor light-emitting element shown in FIG. 9, it has been also desired to increase further the light emission efficiency. In case the light transmittance of the transparent conductive film 25′ is raised to increase further the light extraction efficiency, the electric conductivity is difficult to maintain. Therefore, the light emission efficiency is difficult to increase.
A semiconductor light-emitting element shown in FIG. 10 has been suggested that includes a p-type GaN film 24′, a light-emitting layer 23′, an n-type GaN film 22′, a cathode 4′ formed on the flat surface in the center of the upper surface of the n-type GaN film 22′, an anode 5′ formed on the lower surface of the p-type GaN film 24′, and a support substrate (not shown in the figure) joined to the lower surface of the anode 5′ via a joining layer (not shown in the figure) composed of a conductive material (see, for example, Japanese Patent Application Laid-Open No. 2008-60331). In such a semiconductor light-emitting element, in order to increase the light extraction efficiency, a fine peak-valley structure is formed by way of crystal anisotropic etching using a KOH solution outside a formation portion of the cathode 4′ on the upper surface of the n-type GaN film 22′. The anode 5′ of such semiconductor light-emitting element is composed of a contact ZnO film 5a′, a Schottky ZnO film 5b′ that is in contact with the p-type GaN film 24′ only in the projection region of the cathode 4′, and a current diffusion ZnO film 5c′. 
In the semiconductor light-emitting element shown in FIG. 10, the cathode 4′ is formed on the flat surface of the n-type GaN film 22′, thereby making it possible to inhibit light absorption by the cathode 4′. Furthermore, since the contact resistance in the anode 5′ with the p-type GaN film 24′ in the projection region of the cathode 4′ is larger than the contact resistance with the p-type GaN film 24′ in the region outside this projection region, the concentration of electric current immediately below the cathode 4′ can be relaxed, the ratio of light absorbed or blocked by the cathode 4′ can be reduced, and light extraction efficiency can be increased.
With the object of increasing the light extraction efficiency, a semiconductor light-emitting element has recently been suggested in which a light-emitting layer having an n-type GaN film and a p-type GaN film is joined to a base formed from transparent and conductive n-type ZnO, and the base is processed into a hexagonal pyramidal shape by way of crystal anisotropic etching utilizing the dependence of etching rate on crystal orientation (see, for example, the following non-patent document: “Matsushita Denko to UCSB-no Shingata LED, Gaibu Ryoshi Koritsu 80% Mezasu” (New Type LED by Panasonic Electric Works and UCSB; Targeting at Achieving 80% External Quantum Efficiency) (Nikkei Electronics, Nikkei BP Sha, Feb. 11, 2008, p. 16-17)).
The semiconductor light-emitting element disclosed in this Non-Patent Document is provided with the light-emitting layer and the base formed of the hexagonal pyramidal n-type ZnO substrate joined to the light-emitting layer, wherein an anode is formed on the lower surface of the base, a cathode is formed on the lower surface of the n-type GaN film of the light-emitting layer, and the anode and the cathode are joined to mutually different wiring patterns (conductive patterns) of the mounting Substrate by use of bumps.
However, in the semiconductor light-emitting element of the configuration shown in FIG. 10, the light is assumed to be taken out mainly from the fine peak-valley structure of the n-type GaN film 22′. Therefore, the light emitted from the light-emitting film 23′ towards the p-type GaN film 24′ is absorbed by a joining layer, or reflected by the joining layer to fall on the light-emitting layer and be absorbed thereby. The resultant problem is that the light emission efficiency is low.
Further, in the semiconductor light-emitting element disclosed in the aforementioned non-patent document, the refractive index of the base is less than the refractive index of the p-type GaN film. Therefore, the light with a small incidence angle on the joining surface of the base and the p-type GaN film, from among the light generated by the light-emitting layer, is not introduced into the ZnO. Therefore, further increase in light emission efficiency has been desired.